In practice, there is generally driven in roller mills the grinding table which drives the grinding rollers via the grinding bed. However, this leads to significant fluctuations in performance levels and consequently to high loads on the drive train with the result that the drive power which can be reliably transmitted is very limited.
DE 38 01 728 describes a roller mill in which a drive motor is associated with each grinding roller. Furthermore, the grinding table has an auxiliary drive.
It has also already been suggested in DE 197 02 854 A1 to drive the rollers. It was also set out therein that the individual grinding rollers are, on the one hand, coupled with each other via the grinding table and the grinding stock or the grinding stock bed which is located thereon and, on the other hand, can have very different power consumptions which can be attributed, for example, to different rolling diameters on the grinding table (position of the force application point/radius), different effective diameters of the individual grinding rollers (for example owing to wear) and to different characteristics of the grinding stock being drawn in during interaction on the grinding table and grinding roller.
Even small speed variations between individual grinding rollers bring about relatively high power fluctuations in the drives. This can lead to the grinding rollers being constantly accelerated or decelerated, that is to say, the individually driven grinding rollers work against each other which leads to a significantly increased power or energy requirement during communition operation.
In DE-A1-197 02 854, it is therefore proposed that the operational fluctuations between the individual rotary drives of all the driven grinding rollers be compensated for by a common load compensation adjustment system. However, in the case of dynamic transmission changes between the grinding table and grinding roller, the power consumptions of the drives are very different.
DE-A1-10 2006 050 205 further discloses a roller mill whose grinding table is driven by an arrangement of more than two drives. For the drives, there are provided electric motors which are supplied by means of frequency converters and by means of which the speed and torque are adjusted. The frequency converters are organised in accordance with the master-slave principle in order to ensure that all the drives operate in a synchronous manner. However, these frequency converters result in high costs for the drive train.
DE 201 06 177 U1 relates to an edge mill with an additional drive which has a direct torque adjustment system.